The present invention relates generally to data compression systems and more particularly to a method and apparatus for reducing the number of data bits to be stored in a block of data generated during the operation of a terminal device without losing the informational content of the data, in which the time of day is part of the data. In modern on-line data processing systems in which data is generated by remote data processing devices, cost is always a factor in the purchase of the system. One of the areas of cost is the amount of memory associated with the terminal device. In order to fully utilize the memory capacity found in today's terminal devices, various methods for compacting the data when stored in the memory has been devised. For example, in U.S. Pat. No. 4,021,782, the data is compacted by varying the length and number base of the data. In U.S. Pat. Nos. 3,694,813, 3,717,851 and 3,925,780, data processing techniques using variable length codes to encode data in order to reduce the amount of data that is to be stored are disclosed. Since all of these techniques are directed for use with a central processing unit, their use by a stand-alone data terminal device which generates data independently of the processing unit would not be econcmically feasible.
It is therefore a primary object of this invention to provide a low-cost data compression apparatus capable of reducing the amount of data that is to be stored in a memory unit and which has been generated as a result of a data terminal operation without losing any of the data transactional detail, the reduced data being used to restore the original data when the data is transferred to a central processing unit.